Case airflow advice needed!

KungFuSpaghetti · 10 Jan 2018 at 09:14

Hi all, I'm having a bit of a headache with how to maximise airflow in my case to get the best configuration since adding a GPU AIO water kit.

I have a Fractal Design Define C case and I have a load of case fans for this now, some of which may now be redundant... I'm running a Noctua d14 CPU cooler with the exhaust fan direct behind it, so the d14 fans are blowing air through in a straight line to vent through the rad and out the back. I can also only mount my GPU rad at the front of the case, as it will not fit at the top of the case due to the d14. I've started redoing the whole airflow, so at present I've got the rad mounted at the front of the case with the two fans attached to the rad blowing air through the rad and out of the front.

My dilemma now is for the rest of the system. I have a total of 5 120mm case fans, so I cant fit all of them so just trying to decide what best to do. I have the vent at the top of the case off now, so I could fit two fans here, either drawing air in or out, but not sure how best to tackle this. I have currently mounted one fan which will draw air into the case from the top and blow directly onto the VRMs and into the d14, not sure if this is a good idea with it pulling air in and then blowing it through and across itself to vent out? If that is fine, then would 2 fans be better than one, or should I have both of these fans drawing air out?

The other option I have is a bottom case fan, I could in theory pull air in from underneath the case as heat rises, then it would eventually get to the d14 and be vented out of the back?

The next dilemma is, I only have 4 inputs for 3 pin PWM fan connections on my motherboard. Is it safe to have 8-10 fans on splitters running over 4 motherboard connections?

I know it would probably help if I had pictures, so I'll try and get some later if it would help!

trawetSluaP · 10 Jan 2018 at 10:18

Hi,

If it were me I'd have the GPU rad fans as intake at the front of the case and then top fans as exhaust. You could then add an intake fan to the bottom to increase the cool air getting into the case.

Regarding the headers, you could look into grabbing a PWM Splitter like Swiftech produces. It uses a sata power connector to power the fans. Just be aware that all fans would then be running at the same speed. alternatively you could use conventional fan splitter cables.

KungFuSpaghetti · 10 Jan 2018 at 10:21

I did consider this too, but if the rad fans are pulling air in through the rad won't I just be pulling in hot air? I've no idea how warm these rads get as I've not powered it up yet through fear lol.

As for the fans in general I world prefer them running pwm, but is it safe having that many fans powered through 4 motherboard connectors?

trawetSluaP · 10 Jan 2018 at 10:34

KungFuSpaghetti said:
I did consider this too, but if the rad fans are pulling air in through the rad won't I just be pulling in hot air? I've no idea how warm these rads get as I've not powered it up yet through fear lol.

As for the fans in general I world prefer them running pwm, but is it safe having that many fans powered through 4 motherboard connectors?

Only way to find out is to power it on. you may see a hit in CPU temps increasing as the CPU cooler might get some of the hot air expelled from the rad but you will see GPU temps drop a little as the cooler will benefit from the coll air it is pulling from the outside of the case.

With regard to the fans on a single header I'm not sure if 4 would be too much for a single header, hopefully a more knowledgeable member can inform us. however, if you choose to use a PWM splitter like Swiftech's it's powered by your PSU and not the motherboard so that avoids this issue.

KungFuSpaghetti · 10 Jan 2018 at 11:04

Yeah I can try it with the rad having air pulled through and into the case or expelled out and see which works best. My CPU generally only gets to about 60 degrees under load in synthetic benchmarks, so shouldn't be much of an issue.

Think that swiftech PWM splitter might be a good option either way though.

Pocah · 11 Jan 2018 at 07:05

If the GPU radiator is on the front and can't be changed then you can either have it as an intake which will warm the inside of the case or an exhaust. Generally it is better to have radiators as intakes because that's the best for the device you are trying to cool. Of course that way it will heat the inside of the case, though, and so in your case will affect CPU and mother board temps.
If you have it as an intake it's best to have a second intake fan somewhere flooding the case with cold air. You may also find some benefit to an exhaust fan, but usually it's best to have more intake fans than exhaust fans so you maintain positive air pressure in the case.
I think it's perfectly valid to have the GPU as an exhaust since it creates more heat than anything else. You could also have the rear case fan as an exhaust for the CPU cooler. However, you will then somewhat struggle to maintain positive pressure. You will need at least two fans blowing air in to the case to ensure positive pressure and you also have to link them to the gpu cooler and exhaust fan so that they provide at least as much air in to the case as they are blowing out. Maybe even three fans. The way I achieve that is to put one input fan on a splitter from the GPU exhaust radiator fan and the other on a splitter from case exhaust. That way they will be in step with the total exhaust. You may even add a third to make sure the pressure is positive. You may not be worried about positive pressure though, some people just don't care about that.
You can buy fan splitters that have their own power connections so they place no load on the header, but you shouldn't need them. Another alternative is to buy something like a Corsair Commander Pro, with which you can precisely control all the fans.

doyll · 11 Jan 2018 at 14:50

Problem with using a CLC as intake is as Pocah said, it heats air supply to other components .. and trying to add other fans to supply cool air to components in the case requires exhaust vent area with and without fans to be more then intake vent area with fans .. so if we have 2x 120mm fans on radiator intake and 1x 140mm fan elsewhere as intake we now need at least 2x 120mm fanned exhaust vents and 1x 140mm fanned exhaust vent to match intake airflow to exhaust airflow .. because the case will only flow as much air as the smaller of the two. Hope that makes sense.